"We are swimming from Germany to Austria."
Translation:Wir schwimmen von Deutschland nach Österreich.
You're slightly mistaken.
Ich komme aus Deutschland = "I come from Germany" - I was born and raised there
Ich fahre von Deutschland nach... = "I drive from Germany to..." - I start my journey there
But I suppose you could also have:
Ich fahre aus Deutschland heraus = "I drive out of Germany"
Is a preposition "tied" to a verb, as you have "fahre von" and "komme aus" in your response above? The implication is that it would be "schwimmen von" for the sentence to be translated here. I use the rules for aus and nach, vor and zu from what I have learned over the years with Duo and other sources, including the table below. https://www.studyblue.com/notes/note/n/nach-vs-zu-and-aus-vs-von/deck/6051428
The prepositions aren't tied to verbs, they just have different meanings.
“aus” means from in the sense “coming from”. A person “aus Italien” is an Italian person. You can also use it with “kommen” (“ich komme aus Berlin” — “I'm from Berlin”). Of course it also has other meanings, but this is the one inferred when used in conjunction with a country or city. It can also mean “out of”.
“von” indicates origin of a movement, especially in expressions like “from ... to ...”, which is always “von ... nach/zu ...”.
You can't always translate word by word. Particularly prepositions are used rather differently in different languages, so every preposition usually has an abundance of possible translations. In order to describe movements towards a country or a city, the preposition is always "nach".
It describes something different. So, for the rare case that really someone swims through the Bodensee, you swim or travel to go from one country to another and then its always nach. This always includes entering the estimated country. So you try to enter austria via swimming.
Ich renne von Dänemark bis Österreich (or also von Dänemark bis nach Österreich), describes something different. It would describe that you start running in denmark and you run until you reach the austrian border. This does not include the intention of traveling/entering austria. It just uses austria to describe the distance of running. Such a construction would be more common in scenarios like. The distance from denmark to austria is X km. Die Distanz von Dänemark bis Österreich beträgt x km.